Vajna was a confidant of Prime Minister Ferenc Szálasi, the Hungarian fascist party leader and founder of the extreme right "Party of National Will", which later became the Arrow Cross Party. Vajna took office as Interior Minister in October 1944 and served until March 1945.

While responsible for internal affairs, Vajna took a number of actions against Hungarian Jews. In cooperation with requests from German officials such as SS officer Edmund Veesenmayer, Vajna moved quickly to deport Jews in areas under Hungarian control to the Third Reich, where they were used as slaves and many were ultimately killed. As many as 76,000 Jews were delivered into Nazi hands through the end of 1944[citation needed].